San-Lin Young

Structure and photovoltaic properties of ZnO nanowire for dye-sensitized solar cells

Aligned ZnO nanowires with different lengths (1 to approximately 4 μm) have been deposited on indium titanium oxide-coated glass substrates by using the solution phase deposition method for application as a work electrode in dye-sensitized solar cells (DSSC). From the results, the increases in length of zinc oxide (ZnO) nanowires can increase adsorption of the N3 dye through ZnO nanowires to improve the short-circuit photocurrent (Jsc) and open-circuit voltage (Voc), respectively. However, the Jsc and Voc values of DSSC with ZnO nanowires length of 4.0 μm (4.8 mA/cm2 and 0.58 V) are smaller than those of DSSC with ZnO nanowires length of 3.0 μm (5.6 mA/cm2 and 0.62 V). It could be due to the increased length of ZnO nanowires also resulted in a decrease in the transmittance of ZnO nanowires thus reducing the incident light intensity on the N3 dye. Optimum power conversion efficiency (η) of 1.49% was obtained in a DSSC with the ZnO nanowires length of 3 μm.

Influence of Y-doped induced defects on the optical and magnetic properties of ZnO nanorod arrays prepared by low-temperature hydrothermal process

One-dimensional pure zinc oxide (ZnO) and Y-doped ZnO nanorod arrays have been successfully fabricated on the silicon substrate for comparison by a simple hydrothermal process at the low temperature of 90°C. The Y-doped nanorods exhibit the same c-axis-oriented wurtzite hexagonal structure as pure ZnO nanorods. Based on the results of photoluminescence, an enhancement of defect-induced green-yellow visible emission is observed for the Y-doped ZnO nanorods. The decrease of E2(H) mode intensity and increase of E1(LO) mode intensity examined by the Raman spectrum also indicate the increase of defects for the Y-doped ZnO nanorods. As compared to pure ZnO nanorods, Y-doped ZnO nanorods show a remarked increase of saturation magnetization. The combination of visible photoluminescence and ferromagnetism measurement results indicates the increase of oxygen defects due to the Y doping which plays a crucial role in the optical and magnetic performances of the ZnO nanorods.

Effect of annealing temperature on exchange coupling in NiFe∕FeMn and FeMn∕NiFe systems

Most studies on exchange bias in spin valves are for antiferromagnetic/ferromagnetic structures, and Fe[50]Mn[50]∕Ni[79]Fe[21] is widely used. The results of the exchange-bias field (Hex) and coercivity (Hc) as a function of the annealing temperature in NiFe∕FeMn and FeMn∕NiFe systems are given in the study. We prepare two types of films, type I: substrate/∕Ta∕NiFe∕FeMn∕Ta and type II: substrate/Ta∕FeMn∕NiFe∕Ta, respectively. Annealing was performed at 150–450°C under 720Oe for 2h, Hex and Hc of type I samples increase slightly with the increase of the annealing temperature. But Hex and Hc of type II samples increase rapidly after annealing over 300°C, then decrease after annealing at 375°C. The strong exchange-bias field and low coercivity were exhibited for type I samples, where NiFe is the buffer layer and is also the pinned layer. In type II samples, the increase in the exchange-bias field is attributed to the altered interface of FeMn∕NiFe due to interdiffusion. The interpretation of the fluctuation ...

Structural Dependence of Photoluminescence and Room-Temperature Ferromagnetism in Lightly Cu-Doped ZnO Nanorods

Well-defined 1-D ZnO and ZnO:Cu semiconductor nanostructures have been fabricated by a low temperature solution process. Cu (0.073 nm) is chosen as a dopant due to the similar ionic radius with Zn (0.074 nm). The radius of ZnO:Cu nanorods observed by FE-SEM is lager than that of pure ZnO which indicates the growth rate of the nanorods can be obviously enhanced by the light doping of Cu. The XRD patterns of both compositions with single diffraction peak (002) show the same wurtzite hexagonal structure. Photoluminescence spectra show a red-shift of the UV emission peak position and a decrease of the luminescence intensity in green-yellow region. From the room temperature hysteresis loop, ferromagnetism is observed and the saturation magnetization decreases with the increase of the Cu concentration for ZnO:Cu nanorods.

Improved Energy Conversion Efficiency of TiO2 Thin Films Modified with Ta2O5 in Dye-Sensitized Solar Cells

Tantalum-doped TiO2 thin films [(TiO2)1-x(Ta2O5)x, x=0–0.8%] were prepared on fluorine-doped tin oxide (FTO)-coated substrates by sol–gel technology for uses in dye-sensitized solar cells (DSSCs). The effects of Ta content on the growth and properties of the TiO2 thin films were investigated. The crystallization and microstructures of the thin films were examined by X-ray diffraction, scanning electron microscopy, and Brunauer–Emmett–Teller analyses. The performance of DSSCs based on Ta-doped TiO2 thin films was also studied. From the obtained results, the increases in Jsc and Voc may be due to the increased electron concentration of TiO2 thin film and the flat-band potential of the TiO2 shifted by tantalum doping, respectively. The optimum properties of DSSCs of Voc=0.68 V, Jsc=7.84 mA/cm2, FF=45.1%, and η=2.4% were obtained using the Ta-doped TiO2 thin film with x=0.5%.

Thickness effect of sputtered ZnO seed layer on the electrical properties of Li-doped ZnO nanorods and application on the UV photodetector

Well-defined Zn0.9Li0.1O nanorods were hydrothermally synthesized at the low temperature of 90°C on the sputtered ZnO seed layer in different thickness, 20 nm and 50 nm. The x-ray diffraction patterns of both samples with a single diffraction peak (002) showed the same wurtzite hexagonal structure. The length and diameter of the nanorods were both increased from 1.12 μm to 1.47 μm and 95 nm to 113 nm, respectively, while increasing the sputtered ZnO seed layer thickness from 20 nm to 50 nm. The optical properties were influenced by the presence of oxygen vacancies induced by Li doping in the Zn0.9Li0.1O nanorods. Besides, p-type ZnO-based semiconductor nanorods were obtained by the doping of Li into ZnO. Finally, the UV photodetectors with (p-Zn0.9Li0.1O nanorods)/(n-Si substrate) structure were also achieved. The I-V characteristics of the UV photodetector with p-ZnO:Li nanorod/n-Si structure were also measured. The UV illumination/dark current ratio of the photodetectors with different seeded layer, 20nm and 50nm, were also measured as 201% and 364%, respectively.

Substrate Effect on Characteristics of PbZrxTi1−xO3 (PZT) Film

The paper presents the effect of substrates on the characteristics of PbZrxTi1−xO3 (PZT) thin film fabricated by sol-gel spin coating technology. The PZT sol-gel is prepared by mixing PZT powder and PZT solution, and fabricated on various substrates, including copper (Cu), alumina (Al2O3), stainless steel (SS) and titanium (Ti). The dielectric characteristics and orientation of films had been measured by SEM, LCR meter, XRD for comparison. The experimental results indicate that the substrates having the similar characteristics with PZT film would result in better crystallization, charge storage capacity and energy transfer efficiency of film.

Variable-Range Hopping and Thermal Activation Conduction of Y-Doped ZnO Nanocrystalline Films

ZnO and Y-doped ZnO nanocrystalline films were separately fabricated on the glass substrates by sol-gel spin-coating method. X-ray diffraction patterns of the films show the same wurtzite hexagonal structure and (0 0 2) preferential orientation. Scanning electron microscope images show that grain size and thickness of the nanocrystalline films decrease with increasing doping concentration. The decrease of optical bandgap with the increase of Y doping is deduced from the transmittance spectra. Temperature-dependent resistivity reveals a semiconductor transport behavior for all ZnO and Y-doped ZnO nanocrystalline films. The resulting conductivity originates from the combination of thermal activation conduction and Mott variable-range hopping (VRH) conduction. In the high-temperature range, the temperature-dependent resistivity can be described by the Arrhenius equation, σ (T) = σ0 exp[ -(Ea/kT)], which shows the thermal activation conduction. The activation energy Ea increases from 0.47 meV for ZnO film to 0.83 meV for Zn0.98Y0.02O film. On the contrary, in the low-temperature range, the temperature-dependent resistivity can be fitted well by the relationship, σ(T) = σh 0exp[-(T0/T)1/4], which indicates the behavior of Mott VRH. The results demonstrate that the crystallization and the corresponding carrier transport behavior of the ZnO and Y-doped ZnO nanocrystalline films are affected by Y doping.

MAGNETIC PROPERTIES OF La-DOPED AND Cu-DOPED ZnO NANOWIRES FABRICATED BY HYDROTHERMAL METHOD

La-doped and Cu-doped ZnO nanowires have been prepared to compare the substitution effect on the microstructural and magnetic properties. The XRD patterns of both compositions with single diffraction peak (002) show the same wurtzite hexagonal structure. The growth rate of the ZnO nanowires were enhanced by Cu doping, which were different from the suppression of growth rate by La doping. Room temperature ferromagnetism is observed for all ZnO, Cu-doped ZnO and La-doped ZnO nanowires. The saturation magnetizations are 0.102, 0.232 and 0.04 emu/g for ZnO, Cu-doped ZnO and La-doped ZnO nanowires, respectively. The results showed that the ferromagnetism is restrained by Cu doping, but enhanced by the La doping.

Structural, Electrical, Magnetic and Resistive Switching Properties of the Multiferroic/Ferroelectric Bilayer Thin Films

Bi0.8Pr0.2Fe0.95Mn0.05O3/Bi3.96Gd0.04Ti2.95W0.05O12 (BPFMO/BGTWO) bilayer thin films with Multiferroic/Ferroelectric (MF/FE) structures were deposited onto Pt(111)/Ti/SiO2/Si(100) substrates by using the sol-gel method with rapid thermal annealing. The BPFMO/BGTWO thin films exhibited well-saturated ferromagnetic and ferroelectric hysteresis loops because of the electro-magnetic coupling induced by the MF/FE structure. The remnant magnetization (2Mr) and remnant polarization (2Pr) were 4.6 emu/cm3 and 62 μC/cm2, respectively. Moreover, the bipolar I-V switching curves of BPFMO/BGTWO bilayer thin films resistive random access memory (RRAM) devices were discussed, and investigated for LRS/HRS.